Field of the Invention
The present invention relates to an optical apparatus and a drive controlling method, which provide autofocus on a moving object (moving-object AF) using an image-pickup optical system configured to correct a variation of an image plane associated with a magnification variation.
Description of the Related Art
The improved precision of the moving-object AF has recently been increasingly demanded. Japanese Patent Laid-Open No. (“JP”) 2009-128614 proposes a camera configured to acquire a driving target position of a focus lens by using a detected defocus amount for a feedback value to be sent to a controller, to correct the driving target position based on the focus lens potion at the acquisition time, and to control a prediction of a moving object based on the corrected driving target position.
It is known as a tracking control in a rear-focus type magnification varying optical system to correct a variation of an image plane associated with a magnification variation by moving a focus lens, as the variable-magnification lens is moved, and to maintain the in-focus state. The tracking control utilizes pre-stored information of an electronic cam (tracking curve) that indicates the in-focus position of the focus lens for the position of the variable-magnification lens (or focal length) for each object distance. As the variable-magnification lens is moved, positioning of the focus lens is controlled along the electronic cam. JP 2013-242353 discloses one example of the electronic cam in FIG. 4.
However, due to the performance of the motor for driving the focus lens, the focus lens may not be able to be follow the electronic cam immediately and a time lag occurs until the focus lens follows the electronic cam. A blur occurs while the variation of the image plane is being corrected. JP 2009-128614 does not consider this blur. As a consequence, when the camera body sends a focus driving instruction based on a detection result of a focusing state by a phase difference detecting method, the in-focus precision lowers because the blur influence that is eliminated at the time of sending the driving instruction is contained in the driving instruction.